Search only in a specific Category

What does “a specific tag that is part of that category” mean, exactly?

[searchform cat="1" post_tag="tag_a"]

This shortcode creates a search form that will only search posts within category 1 that have the tag “tag_a”. Is this what you need?

yes that does answer part of my question but to clarify further, is there a way to have a multiple search widget that search different categories.

For example:
I have a category and a series of posts for How To and I want a search widget on these pages to only search within the How To category

I have a category and a series of posts for FAQ and I want a search widget on these pages to only search within the FAQ category

Is this possible?

Yes, you can use shortcodes to create multiple search forms with different parameters.

If you want the same search form to target different parts of the site depending on the context, that’s also possible, it just requires that the search form parameters are modified on the fly.

If you don’t know how to do that, that’s something every WP developer will be able to do for you; there’s nothing Relevanssi-specific about this, the parameters Relevanssi accepts are common WordPress WP_Query parameters, and every WP developer should be able to use them.

Is your plugin compatible with Elementor?

Yes. Elementor has these instructions for customizing the search results, and if you do a search results archive this way, that doesn’t work at all with Relevanssi. But as long as you use a standard WordPress search results template, Elementor and Relevanssi work well together.